The present invention relates to telecommunications equipment generally, and more specifically to adapters for connecting a cable to an enclosure, such as a building entrance protector.
A building entrance protector (BEP) enclosure houses the physical interface between the nodes of a local telecommunications network and a telecommunications cable. For example, a BEP enclosure may house the interface hardware between the telephones of an office building and an exterior telephone cable having a number of twisted copper pairs that carry the voice signals for those telephones. A BEP enclosure is typically mounted in the basement or first floor of the office building. A BEP enclosure may also be used to house the interface hardware for systems based on fiber optical communications. Similarly, BEP enclosures may be used with telecommunications systems carrying signals other than just telephone voice signals.
A BEP enclosure provides two main functions: (1) it houses the hardware that provides connections between a cable and the individual nodes (e.g., telephones) of a local network; and (2) it houses the hardware that provides electrical isolation between the cable and the local network. Electrical isolation is intended to prevent any high voltages and/or high currents that may exist from time to time in the cable from reaching the local network. For example, a BEP enclosure will house isolation components designed to protect telephone users from lightning striking a telephone cable. Such electrical isolation is typically provided by 5-pin plug-in protectors that quickly connect signals to ground upon detection of sufficiently high voltages or currents. Building entrance protectors are described in U.S. Pat. Nos. 5,803,292 and 5,907,127, which are expressly incorporated by reference herein.
The end cap of a BEP may include one or more cable ports, which extend outwardly from the end cap. The cable port allows the cable to enter into the enclosure. A cold shrink tubing is normally used to seal around both the cable and the cable port. Cold shrink tubing is described in U.S. Pat No. 3,515,798, U.S. Pat. No. 4,871,599, and U.S. Pat. No. 5,670,223, all of which are expressly incorporated herein by reference. The cold shrink tubing secures the cable to the BEP housing, aligns the cable, and provides a seal to protect the fiber enclosure from the outdoor environments.
Different size cables require different size ports. To perform its functions properly, a piece of cold shrink tubing must have a diameter that is suitable for the cable. A given size of cold shrink tubing does not have the range of shrinkage ability that is provided by heat shrink tubing. Thus, a given piece of cold shrink tubing cannot handle all cable sizes. A series of cold shrink tubing sizes are needed to seal around a wide range of cable sizes. For example, the Minnesota Mining and Manufacturing Co. of St. Paul, Minn. sells a series of products, numbers 4626L (or S) through 4631L (or S).
If the cable port size is too large relative to the cable size, the cable does not remain aligned straight within the port. A wobbly cable could result in damage to the exposed fibers within the enclosure. To alleviate this problem, different sized ports may also be required to maintain a firm hold on the fiber cable, typically, small, medium and large. To fit an equal number of small, medium and large ports within the limited space of the enclosure end cap, the number of any port size would be reduced to one third of the total number of cable ports.
FIGS. 1 and 2 show a multi-size adapter 10 according to the prior art. Adapter 10 can accommodate a small, medium or large cable. Adapter 10 has three cable ports 11, 13 and 15, with respective cylindrical side walls, 16, 20 and 24. Cable ports 11, 13 and 15 are sized to accommodate large, medium (not shown) and small (not shown) cables respectively. For each cable size, a different portion of adapter 10 is cut away to leave an appropriately sized cable port 11, 13 or 15 for the cable being accommodated.
For example, FIG. 3 shows an adapter that has been cut between the ledge 17 and the flat surface 18 of FIG. 2 to accommodate a large cable 28. The portion of the adapter 10 to the left of ledge 17 in FIG. 2 (including side walls 20 and 24, and flat surfaces 22 and 26) is cut away and discarded. The remaining portion of adapter 10 includes a mounting flange 12 and a cable port 11 having side wall 16 with a size that is matched to the cable 28 and the cold shrink tubing 30. The adapter 10 is mounted to the end cap of a BEP 50 using fasteners 14. The cold shrink tubing 30 with its core (not shown) still intact is placed over the cable port 11. The cable 28 is fit through the cold shrink tubing 30 and the cable port 11 of adapter 10. The core of the cold shrink tubing 30 is removed, and the tubing collapses to form a sealed joint around the cable port 11 and the cable 28.
As best seen in FIG. 2, the adapter 10 has a length that is three times the length of an adaptor (not shown) that is designed to accommodate only a single cable size. This may be a disadvantage if, for example, it is desired to install more than one BEP 50 in a small space, or if it is desired to install a BEP near the floor. In either case, the length of the adapter 10 may exceed the available space. A more compact adapter is desired.
The present invention is an adapter for securing a cable to a housing. The adapter has a flange that is attachable to the housing. A plurality of concentric cable ports are connected to the flange. Each cable port has a side wall. The side wall of each cable port overlaps a side wall of an adjacent one of the plurality of cable ports.
Another aspect of the invention is a method for securing a cable to a housing. An adapter is attached to the housing, the adapter having a plurality of concentric cable ports, each cable port having a side wall, the side wall of each cable port overlapping a side wall of an adjacent one of the plurality of cable ports. A portion of a selected one of the cable ports is cut, so as to remove any cable port that is smaller in diameter than the selected cable port. The cable is secured to the selected cable port.